Our studies demonstrate ?depressions? to dilate during secretion, returning to their resting size following completion of the process. Exposure of cells to cytochalasin B, a fungal toxin that inhibits actin polymerization, results in a decrease in size of ?depressions?, to be the sites where vesicle may dock and fuse to release their contents. We seek to test this hypothesis and to gain further understanding of these structures and their biochemical composition. In view of this, my Specific Aim is to determine the biochemistry of ?pits? and ?depressions?. To understand the biochemistry of ?pits? and ?depressions?, the AFM cantilever will be used as a nanosurgical tool to isolate them for biochemical analysis using mass spectroscopy. Since actin regulates ?depressions? morphology, actin antibody affinity columns will be used to isolate and characterize ?depressions? morphology, actin antibody affinity columns will be used to isolate and characterize ?depressions? from solubilized acinar cell plasma membrane preparations. These studies will further our understanding of the exocytotic fusion machinery in pancreatic acinar cells, contributing to our understanding of this vital cellular process.